Hibernate多对多的案列（学生和老师）

多对多

学生和老师的问题就是明显的多对多问题，这里我们采用学生控制老师，即保存学生的时候保存老师，所以在学生里面设置一个cascade即可。但是由于是多对多问题，所以我们还是要建立一个中间表来存放两方的外键。
学生代码（注解配置）：

package manytomany;

import java.util.HashSet;
import java.util.Set;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.JoinTable;
import javax.persistence.ManyToMany;
import javax.persistence.Table;

import org.hibernate.annotations.Cascade;
import org.hibernate.annotations.CascadeType;

@Entity
@Table(name="t_student")
public class Student {
	@Id
	@GeneratedValue(strategy=GenerationType.IDENTITY)
	private int id;
	private String name;
	@ManyToMany(targetEntity=Teacher.class)
	
	//使用jointable来描述中间表，并且描述中间表中外键与student，teacher的关系
	//joinColumns用来描述student与中间表的映射关系
	//inverseJoinColumns用来描述teacher与中间表的映射关系
	@JoinTable(name="s_t",joinColumns={@JoinColumn(name="student_id")},inverseJoinColumns={@JoinColumn(name="teacher_id")})
	@Cascade(CascadeType.ALL)
	private Set<Teacher>teachers=new HashSet<Teacher>();
	
	
	public Set<Teacher> getTeachers() {
		return teachers;
	}
	public void setTeachers(Set<Teacher> teachers) {
		this.teachers = teachers;
	}
	public int getId() {
		return id;
	}
	public void setId(int id) {
		this.id = id;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	
	
}

老师代码：

package manytomany;

import java.util.HashSet;
import java.util.Set;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.ManyToMany;
import javax.persistence.Table;

import org.hibernate.annotations.GenericGenerator;
@Entity
@Table(name="t_teacher")
public class Teacher {
	@Id
	@GenericGenerator(name="myuuid",strategy="uuid")
	@GeneratedValue(generator="myuuid")
	private String id;
	private String name;
	@ManyToMany(targetEntity=Student.class,mappedBy="teachers")
	private Set<Student>students=new HashSet<Student>();
	
	
	public Set<Student> getStudents() {
		return students;
	}
	public void setStudents(Set<Student> students) {
		this.students = students;
	}
	public String getId() {
		return id;
	}
	public void setId(String id) {
		this.id = id;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	
	
}

测试代码：建立两个学生同时创建两个老师，

package manytomany;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
import org.junit.Test;

public class testdemo {
	@Test
	public void test(){
		Configuration configuration=new Configuration().configure();
		SessionFactory factory=configuration.buildSessionFactory();
		Session session=factory.openSession();
		session.beginTransaction();
		
		Teacher t1=new Teacher();
		t1.setName("tom");
		
		Teacher t2=new Teacher();
		t1.setName("fox");
		
		Student s1=new Student();
		s1.setName("张三");
		
		Student s2=new Student();
		s2.setName("王五");
		
		s1.getTeachers().add(t1);
		s1.getTeachers().add(t2);
		
		s2.getTeachers().add(t1);
		s2.getTeachers().add(t2);
		
		session.save(s1);
		session.save(s2);
		session.getTransaction().commit();
		session.close();
	}
}